Free/Busy Coexistence

When questioned by partners, on what is the best approach to plan and execute a move of a customer’s email system, from G-Suite to Exchange Online in Office 365, the first questions that I ask are:

How many users do you have to migrate?

Are you going to do a migration in batches (Staged) or cut over all users at the same time?

Usually when there’s a large number of users, the migration in batches is the preferred option. At that point you should consider two things:

How can I automate the mail flow changes

How can I have free/busy coexistence between G-Suite and Office 365

The answer to both questions above is simple: You can automate the mail flow and have free/busy coexistence if you use BitTitan MigrationWiz to move the mailboxes, and the BitTitan automation processes to help you with the changes you need to do per migration batch.

But I want to focus this article more on the free/busy rich coexistence, between Google and Office 365, the value that it brings to your migration and your customer, a technical overview on how it works, and of course how you can configure it.

What is the value on having free/busy coexistence between G-Suite mail and Office 365 Exchange online

User experience. It’s all about the user experience!!! If you are moving a 20k users company from Google to Office 365, you often get questioned about what the migration journey will mean for the end users, in terms of end user experience. When you provide your customer and their end users the ability to have not only mail flow coexistence (that one is mandatory of course) but also calendar free/busy lookup capabilities, you’re giving them the best experience they can have.

I have also seen more and more companies using the BitTitan Google coexistence tool for permanent free/busy coexistence between G-Suite and Exchange Online, so don’t think about it just like an add-on to a migration project, it can be much more than that.

How can I achieve that with BitTitan

Currently BitTitan will allow you to use the Google coexistence tool for free during 3 months, if you use BitTitan MigrationWiz to move all of the mailboxes. If you want coexistence for more than 3 months, or if you’re not using MigrationWiz, you will be quoted a price per user per month.

Note: The statement above was true when I wrote this article. There no guarantee that will be true when you read it so please contNact BitTitan for more information.

Why do I need a free/busy coexistence tool between Google and Office 365

The answer to this is short and simple: the Google Calendar Interop, which is the tool that you need to configure on your Google tenant to query free/busy from Exchange mail systems, cannot query free/busy information, from an Exchange Online mailbox, via the Exchange Web Services API and the Availability Service. Instead it will try and query free/busy information from an Exchange Public folder. The problem is that the newer versions of Exchange don’t support that method anymore.

So in essence, because the Google Calendar Interop hasn’t evolved to match the changes that the Microsoft Exchange product group implemented in the way the free/busy is queried, specifically on the transition from Exchange 2010 to Exchange 2013, you need a translation tool between Google and Office 365. That translation tool is the BitTitan Google Coexistence tool.

How do I configure the BitTitan Google coexistence tool

The answer is, you don’t. You configure the Google Calendar Interop and Exchange Online by creating an Organization Relationship, both to point to the BitTitan Coexistence service, and you also create a MigrationWiz project in the BitTitan portal, so that you can obtain your authentication token from the BitTitan Support (support@bittitan.com). See here the coexistence setup guide.

This is how the Exchange Online Organization Relationship should look like:

And to configure the Organization Relationship:

Download the Coexistence script from the BitTitan setup guide

Add the details to the script as per instructions on the setup guide

Open an Exchange Online PowerShell session

run the script

Verify if the Organization Relationship was properly created by running: Get-OrganizationRelationship |fl

Do I need contacts in each organization for the free/busy to work

No, you don’t need a contact in Google for each user from Exchange Online that you want to query the free/busy, nor you need them in Office 365 for each Google user. You should have contacts in both sides, but to make sure you have a unified Global Address list.

To be clear on this:

Peter@domain.com is a Google mailbox

John@domain.com is an Office 365 mailbox

You don’t need to create peter@domain.com as an Office 365 mail contact

You don’t need to create john@domain.com as a Google mail contact

But again.. you should.. having a unified GAL is usually mandatory and for sure highly recommended.

How do users query the free/busy information

As they do for any other internal user. They open their calendar app and enter the email address of the user on the other system or search for his contact created on the GAL if it exists.

To wrap this up, and please stay tuned for more blog post on this subject coming soon, the rich coexistence (mail flow and free busy) experience, when you’re migrating your customer from Google to Office 365, is very important and also very easy to achieve.

If you have any questions please feel free to reach out. I can help you understand it better as well as configure it.

As always I hope this post was helpful.

PS- The BitTitan coexistence tool also works between Google and Exchange 2010 Sp2+ on premises.

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Disclaimer

The content of this blog is based on my technical knowledge and experience and presented as-is. The solutions and guides presented here are based on the infrastructure i work on. I don't have knowledge about your infrastructure and you should ALWAYS test before implementing solutions into production. All opinions and statements expressed here are solely mine.

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